When a request is proxied it follows two different pipelines (available here)
which apply transformations to both the req and res object.
The first pipeline (incoming) is responsible for the creation and manipulation of the stream that connects your client to the target.
The second pipeline (outgoing) is responsible for the creation and manipulation of the stream that, from your target, returns data
to the client.

selfHandleResponse true/false, if set to true, none of the webOutgoing passes are called and it's your responsibility to appropriately return the response by listening and acting on the proxyRes event

buffer: stream of data to send as the request body. Maybe you have some middleware that consumes the request stream before proxying it on e.g. If you read the body of a request into a field called 'req.rawbody' you could restream this field in the buffer option:

Listening for proxy events

error: The error event is emitted if the request to the target fail. We do not do any error handling of messages passed between client and proxy, and messages passed between proxy and target, so it is recommended that you listen on errors and handle them.

proxyReq: This event is emitted before the data is sent. It gives you a chance to alter the proxyReq request object. Applies to "web" connections

proxyReqWs: This event is emitted before the data is sent. It gives you a chance to alter the proxyReq request object. Applies to "websocket" connections

proxyRes: This event is emitted if the request to the target got a response.

open: This event is emitted once the proxy websocket was created and piped into the target websocket.

Miscellaneous

If you want to handle your own response after receiving the proxyRes, you can do
so with selfHandleResponse. As you can see below, if you use this option, you
are able to intercept and read the proxyRes but you must also make sure to
reply to the res itself otherwise the original client will never receive any
data.

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